Mobile device users often exist in an online or “virtual” world, in which they interact with others, consume information, and conduct business electronically, while operating in the physical world at the same time. Mobile devices are increasingly equipped with sensors and other hardware that can provide information about the user's geographic location. For example, mobile location-based services can be used to generate maps, driving directions, and lists of nearby venues, or to inform other people of the user's current location. However, existing systems generally require the user to take some overt action (such as pressing a button or saying a command) to initiate the use of location-based services, to request information, or to use other services that are available with the mobile device. Particularly when people are busy doing other things, they may not recognize the need for, or remember to request, information or services that could be important or useful to them in the current moment.